Simulation of Main-Chamber Recycling in DIII-D with the UEDGE Code

This report demonstrates a computer simulation model for single-null diverted plasma configurations that include simultaneous interaction of the scrape-off layer (SOL) plasma with toroidally symmetric main-chamber limiter surfaces and divertor plate surfaces. The simulations use the UEDGE code which treats the SOL plasma and recycled neutrals as two-dimensional toroidally symmetric fluids. The spatial domain can include field lines that intersect main chamber surfaces in the far scrape-off layer, which allows the model to include simultaneous plasma contact with both divertor and main chamber targets. Steady-state simulation results for low-density L-mode plasma discharges in DIII-D show that total core fueling increases by about 70 percent when the separatrix-baffle gap is reduced from 6 cm to 3 cm. The additional core fueling is due to neutrals which originate from the ion particle flux incident on the upper outer divertor baffle